1. Field of the Invention
The present invention relates to an organic thin film transistor (TFT) and a method of manufacturing the same, and more particularly, to an organic TFT having an improved contact between source/drain electrodes and an organic semiconductor layer.
2. Description of the Related Technology
Since the development of a polyacetylene polymer which is a conjugated organic polymer having semiconductor characteristics, transistors that use organic materials are actively applied to electronic devices and optical devices. The organic materials have advantages in that they can be synthesized in various ways and can be readily molded to a film or fiber shape, and also have flexibility, conductivity, and low manufacturing costs.
A silicon TFT typically includes a semiconductor layer having source and drain regions doped with a high concentration dopant and a channel region formed between the source and drain regions, a gate electrode located on a region corresponding to the channel region and insulated from the semiconductor layer, and source and drain electrodes respectively contacting the source and drain regions.
However, the silicon TFT having the above structure has drawbacks in that it has high manufacturing costs and is easily damaged by an external impact. In addition, the silicon TFT cannot use a plastic substrate since it is produced by a high temperature process, for example, at a temperature over 300° C.
Flat panel display devices, such as a liquid crystal display device or an organic light emitting display device, include switching devices for controlling pixel operation and TFTs for driving pixels. To provide a flexible display device with a slim and large screen, the use of a plastic substrate instead of a glass substrate has been studied. However, when a plastic substrate is used, as described above, the flat panel display device needs to be manufactured by a low temperature process. Accordingly, it is very difficult to use a plastic substrate for silicon TFTs in flat panel display devices.
Since the above problems may be solved by using an organic film as a semiconductor layer of a TFT, studies about organic TFTs or an organic film to be used as a semiconductor layer have been actively conducted.
FIGS. 1 and 2 are cross-sectional views illustrating portions of a method of manufacturing a conventional organic thin film. Referring to FIG. 1, after a gate electrode 21 and a gate insulating film 25 covering the gate electrode 21 are formed on a substrate 10, a conductive layer 22 is formed on the gate insulating film 25. Referring to FIG. 2, source and drain electrodes 23 are formed by etching the conductive layer 22.
As depicted in FIG. 2, empty spaces are formed at lower end portions of the source and drain electrodes 23 near interfaces with the gate insulating film 25 because the lower end portions of the source and drain electrodes 23 are undercut.
FIG. 3 is a photograph showing a cross-section of source and drain electrodes of an organic TFT. Referring to FIG. 3, an angle between an end surface of the source and drain electrodes 23 and an upper surface of the gate insulating film 25 is about 52° and thus, an empty space is formed under end portions of the source and drain electrodes 23.
In this way, when an organic semiconductor layer 27 is formed after the source and drain electrodes 23 are formed, as depicted in FIG. 4, the organic semiconductor layer 27 may not satisfactorily contact the end portions of the source and drain electrodes 23 due to the spaces 23a and 23b at the end portions of the source and drain electrodes 23. As a result, when a channel is formed in the organic semiconductor layer 27 by applying a predetermined signal to the gate electrode 21, the channel may not satisfactorily contact the source and drain electrodes 23. Accordingly, an electrical signal between the source and drain electrodes 23 may not be transmitted, thereby causing a malfunction.